how compasses work
It turns out that you can imagine the Earth as a huge bar magnet buried inside.
In order for the north end of the compass to point to the North Pole, you must assume that the buried bar magnet has its southern end in the North Pole, as shown in the figure, the right in the picture.
If you look at the world like this then you can see that the normal \"opposite attraction\" rule of the magnet causes the north end of the compass needle to point to the south end of the buried magnet.
So the compass points to the North Pole.
For full accuracy, the bar magnets do not operate entirely along the axis of rotation of the Earth.
It strayed slightly from the center.
This deviation is called Chiwei, and most good maps show what the Chiwei is in different regions (
Because it will change depending on where you are on Earth).
The magnetic field on the surface of the Earth is rather weak.
After all, the Earth is almost 8,000 miles in diameter, so it takes a long way for the magnetic field to affect your compass.
That\'s why the compass needs to have light magnets and non-friction bearings.
Otherwise, there is not enough strength in the Earth\'s magnetic field to turn the needle.
The \"great magnet buried in the core\" analogy can explain why the Earth has a magnetic field, but obviously this is not what really happens.
What exactly happened?
No one knows exactly, but there is an effective theory circulating at the moment.
As mentioned above, the core of the Earth is considered to consist mainly of molten iron (red).
But at the core, the pressure is so great that this overheated iron crystallizes into a solid.
Convection caused by the heat dissipation of the core, as well as the rotation of the Earth, causes the liquid iron to move in a rotating mode.
It is believed that these rotational forces in the liquid iron layer cause a weak magnetic force around the spin axis.
It turns out that since the Earth\'s magnetic field is so weak, the compass is just a detector of a very weak magnetic field generated by anything.
That\'s why we can use a compass to detect small magnetic fields generated by wires carrying current (
Look at how the magnet works. .
Now let\'s take a look at how we can create our own compass.